Wide band amplifier



SIZGIOBG 'IBIIDZO SIIQIOZG WJUIQJU Invetor: Do ald E. Nor` aard Zo His Attorney.

Apri127, 1943.

Reissued Apr. 27, 1943 WIDE BAND AMPLIFIER Donald E. Norg-aard, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York 16 Claims.

Myinvention relates to wide band amplifiers such as those employed for the amplification of video frequency currents used in television.

It has for one of its objects to provide a method and means for producing uniform amplification at all frequencies of such currents from a level only slightly in excess of the undesired disturbing, or noise, currents to substantially higher' level notwithstanding the attenuating effects of such shunt capacities as are usually present.

' In television transmitters, camera tubes are employed which are exposed to the scene to bev televised and which produce currents represent-y ing such scene. These discharge devices have very high impedance such that the currents flowlng therefrom vare not'materially affected by the load Impedance into-'which the tubesv operate.

#These currents may have frequencies extending over the range from zero to about five megacycles. An object of my invention is to provide improved means for producing uniform amplification for these currents throughout this frequency range.

AItiso happens, in the use of the camera tube, thatthe currents produced thereby most faithfully represent the televised scene if adjusted to be as small as possible; i. e., the smaller the cur rents the better they represent the televised picture. Accordingly, one normally adjusts the electron beam of the camera tube to as low intensity as possible and still producev ampliable output currents. Of course, the undesired disturbing, or, so called, noise, currents produced in the amplier chain define the lower limit, it being neces-4 sary that the camera tube output currents be of intensity such that when amplified in the amplifier chain they have an intensity level sufficiently above the undesired noise level. These undesired currents extend throughout the frequency band to be transmitted but the most objectionable of them are in the frequency range below two thou.- sand cycles, or substantially below the line repetition rate employed in the scanning process.

Difficulty is encountered in' effecting uniform amplification over the band of frequencies to Jce amplified because of the low level of thedesired signal wi'th respect to the noise level and because rf'the attenuating effects o'f shunt capacity inherently present throughout the amplifier.

An object of my invention is to overcome this d'fculty and secure uniform amplification throughout the band while minimizing the effects of disturbing currents introduced by the amplider.

The novel features which lI believe to be char- Original No. 2,280,532, dated April 21, 1942, Serial No. 391,378, May. 1, 1941. issue February 27, 1943, Serial No. 477,413

Application for restood by reference to the following description taken in connection with the accompanying drawing, in which Fig. l representsv'van embodiment of my invention,..and Fig. 2a, Fig. 2b, Fig.

-2c and Fig. 2d represent certain characteristics pertaining to its operation. l Y

Referring to Fig. Lof the dravn'rig, I have shown therein an amplification channel extending from terminals I, 2 to terminals 3, d jfThe terminals I, 2 may, of course, be connected to the output terminals of'- a cathode ray, vor camera, tube used in picking up the scene to be televised and these terminals are connected to the input electrodes of an amplifier represented by the rectangle 5.

Fig. 1 includes three rectangles 5, 6 and l, each of which may be taken to represent either asingle stage electron discharge amplifier or a multistage amplifier but in the usual case these rec- 'tangles represent a multi-stage amplifier. Preferably the last stage in each of these amplifiers is of the pentode type, such that it has extremely high internal output impedance and produces output current lwhich is independent of the inagnitude of the load impedance.

The terminal I may be considered to be connected to the input grid of such an amplifier and `the terminal 2 to the cathode through such bias means as may be employed. Operatingpotential for theanodes of thel discharge devices represented by the rectangles 5, 6, and I maybe supplied througn conductors 8, 9,'and I0 respectively to the respective anodes of the different discharge devices.

The network II between rectangles 5 and 6 is the interstage coupling network connected between the anode and the cathode of the last discharge device represented by rectangle 5 and the grid and cathode of the iirst discharge device represented by rectangle 6. Similarly. thenetwork I2 between rectangles G and 'I represents the coupling network connected between the anode and cathode of the last discharge device represented by rectangle 5 and the grid and cathode of the first discharge device represented by rectangle 1. The output network I3 may be connected from the anode and cathode of the last discharge device represented by the rectangle I to the input of any additional stages of amplification that may be required.

of Fig. 2d.

high frequencies.

As previously stated, the camera'tube is one' having extremely high impedance and thus the current produced thereby is not materially Yaffected by the load impedance into which the tube operates. This current, we may consider to be represented by the dotted line A of Hg. 2a. and it is desired that this current be amplied with luniform amplification over the frequency band to produce a voltage at the output terminals 3 and l, which voltage may likewise be represented by a straight line, as indicated by the curve A 'I'his current flows through the impedance between terminals I and 2. This vimpedance is made up of the input capacitance of the first discharge device represented by rectangle which capacitance is indicated by dotted lines at Il, in shunt with such impedances as are present across the circuit, including, for example, resistance such as that indicated at I i and Il through which'blas voltage may be supplied to the grid 4of the r'st stage of the amplifier 5. Such resistance is necessary to produce a limiting nite impedance at low frequencies across the input to the first discharge device of amplifier 5. 'I'he voltage across these terminals produced by the camera tube may, by reasonof these impedances, vary with frequency as indicated, for example, by the curve B of Fig. 2a.

This voltage is as minute as it is practicable to make it and still be amplii'lable in the presence of the noise level of the amplifier, the most objectionable of the noise currents introduced curves is determined primarily by the capacitance Il, the reactance of which at these frequencies is low relative to the resistance of resistor I8. In this range of frequencies current owing between terminals I and V2 flows largely through capacitance Il.

At frequencies below one megacycle the reactance of condensers Il and I5 both increase but since the reactance of capacitance I l is much greater than that of condenser I5 it becomes very high relative to resistance I 8 while the reactance of condenser I 5 remains negligible with respect to resistance I 6.

Since the reactance of condenser I l, at the frequency corresponding to the point Y of curve C, is` already large relative to resistance I6, it, at this and lower frequencies,.has little or no effect upon the shape of the curve C. Similarly, since the reactance of condenser Ii is negligible at the yfrequency corresponding to the point Y, it has little effect upon the shape of the curve C at that point Y. The shape of the curve at this point Y is determined by the resistance I6 and, therefore, curve C in the region of point Y is substantially 'a straight line nearlyr Parallel to the horizontal, or frequency, axis of the graph.

At frequencies below the point Y. the reactance of condenser Il increases and first becomes high relative to resistance II and finally becomes high as compared with I l, which is about A ten times greater than resistance I6. Thus, the

by the amplifier being at low frequency, belowthe line repetition rate, or below two thousand cycles. Y

0f course, one way to correct for the attenuation at high frequency, represented by the curve B is to connect across the circuit, a series combination of inductance and resistance proportioned with respect to capacity I4 to produce lmlform impedance at all frequencies to be amplified. This, however, is not feasible because such inductance and resistance would have such low values that they would so reduce the input voltage available for amplification at all frein the presence of the undesired noise current introduced by the amplifier would be extremely difficult, and, in fact, out of the question.

In accordance with my invention, no attempt is made, in this, part of the circuit, to eect the desired compensation. Instead, a condenser I5 is employedV connected between'the terminal! and a point between the'two resistors IG and I1, this condenser being Vso proportioned relative to resistances I C and I 'I as to produce substantial v,reduction in impedance at the intermediate l frequencies without materially affecting the impedance at either the low frequencies or the Thus, the voltage across capacitance Ii may now, by reason of the presence of condenser I5, be represented by the curve C of Fig. 2a. The attenuation, equal to the difference between curvesB and C, may be effected while still maintaining thesignal intensity above the noise level at all frequencies.

It will be seen that curve C of Fig. 2a lies below curve B to a substantial extent only. in the intermediate part of the range. At the extreme right end of the curve, corresponding to frequencies between about one megacycle and five megaeycles, where condenser I5 has substantially zero reactance, the two curves substantially coincide. In this range of frequencies the shape of both voltage between terminals I and 2 rises with reduced frequency until the point X is reached where the reactancefof condenser Il is so high that it no longer is effective in determining the shape of the curve. Below this point X, curves B and C coincide.

While the use of condenser I5 results in aloss of signal input overa region of intermediate frequencies, it does not reduce the signal input at low frequencies where the noise level is highest. It produces the important advantage of dividing the signal frequency band in two distime por-tiens each having distinctly different until the lower frequency portion which is of higher intensity, becomes of such amplitude that further amplification with a given tube complement results in distortion due to overloading. The lower frequency band may then beattenuated to produce uniform amplification over the entire lower-*frequency portion of the band without loss in amplification in the higher frequency portion of the band, without changing the characteristic relation between voltage and frequency in the high frequency portion of the band, and without reducing the signal level to a point ob- Jectlonably close to the ise level at low frequencies. y

Now the entire band be amplified to such ai level that circuits may be employed lto increase the intensities of currents of the highest fre- This is true atv about one hundred and fifty thousand cycles.

including frequencies up to The voltage represented by the curve C is amplified by the amplifier and produces a current represented by the curve I1 of Fig. 2b at the output of the amplifier 5. This curve I1 has the same shape as the curve C of Fig`r2a since the amplifier 5 has uniform amplification at all fre'- quencies involved and its last stage has high internal impedance to currents in its output circuit as previously mentioned.

, This current is supplied -by amplifier 5 to the network II coupling that amplifier to the amplifier 6. A portion of this current flows through resistance I8 and by-,pass condenser I9. The voltage on the resistance I8 is supplied through coupling condenser to the grid of the first discharge device of the amplifier 6. Between the grid and cathode of this discharge device is connected the series combination of inductance 2I and-resistance 22, which are proportioned relative to theshunt capacitance 23, effective across the input of the amplifier 6 to have uniform impedance throughout the band to electromotive force existing across the combination 2|, 22, and

Connected across condenser 20 is a path comprising resistance 24, condenser 25, and resistance 26, the elements I6, 20, 24, 25, 26, 2| and 22 being proportioned relative to resistances I6 and I1 and capacitance I5 to attenuate th'e low frequency currents in the band, thereby to produce voltage across capacitance 23, which voltage may be represented by the curve Ee of Fig. 2b.

This is effected by so'proportioning the eiements that the sum of resistances I8 and 22 bears the same ratio to resistance I6 that the sum of resistances 24 and 26 bears to resistance lI1. and that the capacitance of condenser I5 bears to the capacitance of condenser 20.

In the path 24, 25, and 26, the resistances 24 and 26 are of equal valueand the condenser 25 is of negligible reactance as compared with the sum of resistances 24 and 26 at the lowest frequency to be amplified; for example, ten cycles per second. In other Words, the path 24, 25, 26

is essentially purely resistive throughout the band. Resistances 24 and 25 are so large that capacity between condenser and ground does not materially affect the transmission characteristics of the channel.

Such proportioning of the elements not only produces uniform amplification over the band 150,000 cycles, but it also renders the system as will later be shown, independent of frequency so that no undesired phase shifts at the different frequencies are produced.

This network produces attenuation at the lower frequencies -to bring about the uniform amplification desired. This attenuation occurs` lhowever, after the amplification of amplifier 5 has been had so that the voltage Es is still above the noise level of amplifier 6 even at low freplified by amplifier 6 in the presence, of course, of such noise currents as are produced by amplifier 6. This amplifier supplies to the network I2 an output current which is represented by the curve Is of Fig, 2c. The signal voltage on'resistance 21 is supplied through coupling condenser 30 to the input of the first discharge device of amplifier 1 between the grid and cathode of which is connected a network comprising an inductance 3l, resistance 32, resistance 33 and bias battery 34, a, condenser being connected between ground and a point between resistances 32 and 33. 'I'he resistance 33 may be variable,

if desired, to correct for changing internal resistance in the source 34 which m'ay be a battery.

Resistor 21', which comprises a portion of the network I2 v,is connected in the path through which unidirectional anode current to the last stage of amplifier 6 is supplied, and has, therefore, a high resistance. Only a small fraction of the lsignal current output of the amplifier 6 flows through this resistor, the remainder of the output current flowing through condenser 30 and the series parallel combi-nation represented by elements 3i, 32, 33, 34, 35 and 36. That is, the impedance looking tojthe right of the juncture of resistance 21 and condenser 30 is considerably lower than the resistance 21 over the entire range of frequencies involved. Condenser 3|! serves as l a blocking condenserto prevent application of unidirectional anode voltage to the grid of the first stage of amplifier 1. This condenser must 'have a reactance substantially-lower than the resistance 21 at the lowest frequency considered, i. e., `ten cycles per second, so that the impedance ,intowhich amplifier 6 works is determined principally by elements 30, 3|, 32, 33, 34, 35 and 36 of the network I2.

Since, as has been shown earlier, the extreme right end of the curves C, Ee and Is is affected by the condenser I4, acting together with resistor I6, the impedance elements 3I and 32 are proportioned in such a manner that the time V constant of the series combination of elements quencies where the disturbing currents are the most intense.

Having produced uniform amplification over the low frequency portion of the band; i.`e., up

to 150,000 cycles, 4it now remains to accentuate the high frequencies sufficiently to produce uniform amplification over the entire band. The band over which accentuation is to be effected and the magnitude` of accentuation required now much less `than would be the case if all of the compensation were to be effected in a single stage of the amplifier.

The voltage represented by the curve Ee is am- 3I and 32 is the same as the time constant of the parallel combination of elements I4 and I6 in order to effect compensation for the phase Aand amplitude of the currents and voltages in4 the upper range of frequencies.

It is important that the frequency at which the network I2 resonates be not lower than 2 to 3 times the upper limit ofgthe amplifier system.; i. e.,l from 10 to 15 megacycles in the embod1ment shown, in order that the resonance effect shall not affect transmission in the band.i This resonance is produced primarily by induct* ance 3l and capacitance 36. Since stray capacity 36 cannot be reduced appreciably, it is necessary that inductance 3| be chosen to resonate with the capacity `36 at a frequency well outside ofi the pass-band of the amplifier. Thus the resistance 32 and the inductance 3|, in general, have exceptionally low values when the circuit is adjusted to give nearly exact compensa'- tion. For example, the 'resistance 32 may be ten ohms and the inductance 3| three microhenries. By so proportioning these elements, uniform.

amplification over the entire band up to the input of amplier 1 may be had.

however, that since the value of resistance 32 l and inductance l3I required lto produce such uniform amplification are very small, they reduce the intensity of the signal over the entire band However, at this point of the circuit, the previous It so happens,

amplification has been sumcient that this loss can be tolerated without reducing the signal level to a point insufficiently above the noise level of amplier 1.

If, in a particular installation, the signals are reduced to a point insufficiently above the noise level of amplifier 'I -then resistance 33 and condenser 35 may be included in the circuit and proportioned relative to resistance 32 in the same way that resistance Il and condenser I are proportioned relative to resistance IE thereby to increase the impedance at low frequencies to produce a voltage across capacitance 3S varying with frequency in the manner illustrated by curve E1 of Fig 2c. Condenser 35 is a substantial short circuit to resistance 33 at the high frequencies to be accentuated but is of suiciently high reactance at the low frequencies where vnoise currents are most objectionable to render resistance 33 eifective in series with resistance 32 to increase the impedance across the channel and bring about the increased low frequency ampliication evidenced by the left end of curve E1.

This voltage E1 is amplified by ampliier 1, which produces a current in its output which may be represented by the curve I1 of Fig. 2d. This current is supplied to the network I3 which is identical in its action to network II. That is, it reduces the low frequency voltage supplied to the terminals 3 and I relative to the high freqency .voltage thereby producing transformation between current-at the terminals I and 2 and voltage at the terminals 3 and I which is uniform at all frequencies in the band of frequencies to be transmitted.V This voltage at terminals 3 and 4 is represented .by the curve A' of Fig. 2d and may be of an' intensity of the order of half a volt, well above noise level at all frequencies, and such that it may be readily amplied to any desired intensity required for the transmittion of the picture represented thereby by modulation upon a carrier wave to be transmitted by radio.

quencies the transmission of which is affected by condenser I5.

Since the network -I I Acom for the yvai'- ,iation in transmission with frequency caused by elements I5, I6, Il, it, of course, is designed relative to that network.

'I'he voltage between terminals I and 2 may be expressed by the following equation:

. E =1 Iza- 26% (i) where I represents the current supplied to the input through terminals I and 2; E represents the voltage between terminals I and 2; R and C represent, respectively, the resistance and capacity of the elements of Fig. 1 designated by the reference numeral written as a subscript after the It will thus be seen that an important feature of my invention resides in the use of the network I5, I6, I1 ai; the input to amplier 5. This network, in effect, divides the frequency band into two portions. the low frequency portion below the frequency represented by point Y of Fig. 2a and the high frequency portion above the frequency' represented by, this point Y. This permits these two portions to be treated separately in the respective networks II and I2, the

network II producing uniform ampliication over the low frequency portion of thev band with an output intensity above the noise level of amplier l and the network I2 accentuating voltages inl the high frequency Aportion of the band. Since, however, the elements required to accentuate the high frequency currents may reduce the intensity of the low frequency currents to intensities unsatsfactorily small, the elements 35 and 33 may be included to maintain the lows suiliciently above the noise level of amplifier 1. Network I3 then brings about the uniform amplification over the band.

l have now generally'set forth the character of my invention. For a more detailed consideration let us rst consider the amplifier 5 and the networks between which it operates, and the portion of the band of frequencies below the point Y of Fig. 2a. This point is at a frequency below the frequencies the transmission of which is aected by capacitance Il. and above the frerespective character; e represents frequency multplied by the constant 21- where 1:31416; and :i representsthe imaginary quantity, V 1.

This nomenclature will be employed throughout the following. Equation l is true only for frequencies below the point Y of Fig. 2a; ije., below around 150,000 cycles.

If G represents the overall mutual conductance of amplifier 5 then the current I1 at the output of amplifierV 5 may be expressed by the following equation:

I1=GE (2) Now, neglecting the capacitance Cn and letting Ln; i. e., the reactance of inductance ZI, equal zero, the impedance Zu of network II u viewed from amplier 5 may be (UC. Laws-g- This equation is true at frequencies at which the reactance of condenser 25 is negligible with respect to the sum, Rael-Ras.

VThe voltage Ee at the input to amplier 6 may be expressed as follows:

E 11R.. +Rl IZ Rn- WC3 i Rdnr-,-

Substituting from Equaon 2 Equation 3 for Zu:

for I1 and from Ra M Simplifying and substituting from Equation 1 for E:

llt. wld-jg) RzeRuaGI R10 Thus, it is found that Es, the input voltage of amplifier B, is independent of frequency below the frequency Y if the above proportionalities be made. Moreover, all of the quantities in Equation 5 are real quantities, which means that there is no phase shift between the current I supplied at terminals I land 2 and the voltage En supplied to amplifier 6 over the frequency range :2

below the point Y.

` This voltage El; is now amplified by amplifier 6 and produces current Ia in network I2 where compensation for the effect of capacitance Il at high frequencies is made.

Now, considering frequencies higher than that corresponding` to point Y, it is necessary. as previously stated, that the time constant of the elements 3| and 32 equal that of the elements I6 and I4 or that The series circuit comprising -nductance 3| and resistance 32, having the same time constant as the shunt circuit comprising capacitance I4 and resistance I6. produces exactly equal and opposite effects upon the transmission through the systenr, and thus, except for the effect of elements 35 and 33 at low frequencies, uniform am- `p1iiication overv the entire band, exists between the terminals I and 2 and the input to amplifier 1f. Elements 35 and 33 may be necessary, however, in order that the signal voltage be large enough at the low frequencies to override the low frequency noise level of the amplifier 1. In that case after the signals have been transmitted through the amplifier 1, the low frequencies may be attenuated sufiiciently to match the high frequencies as indicated by curve A of Fig. 2d and thus produce uniform amplification over the band up to the output terminals and signal intensity at the output well above the noise level of any subsequent amplifiers.

, While in this specification and claims I have referred to wide band amplifiers and have particularly mentioned the frequency band extending from ten cycles to four or five megacycles, .it will, of course, be understood that my invention is readiiyapplicable to-amplifiers operating over much narrower bands of frequencies. My invention finds utility in any amplifier where the signal level to be amplified and the frequency range over which the amplifier must operate are such that the attenuating effects of shunt capacitance cannot be compensated in a single network-of the amplifier without undesirably reducing the signal level.

While I have shown a particular embodiment of myinvention, it will, of course, be understood that I do not wish to be limited thereto since different modifications both in the circuit arrangement and in the instrumentalities employed may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I .claim as new and desire to secure by Letters Patent of the United States is:

1. In an amplifier for producing uniform ratio between input current and output voltage, said amplifier having resistance and capacity in shunt with its input to which said current is supplied said current having frequencies extending over a wide band and having intensities only slightly above the noise level of said amplifier, the method which comprises attenuating currents in the intermediate frequency portion of said band above the frequency of the most intense noise currents of the amplifier without changing the characteristic relation between intensity of voltage on said resistance and capacity andfrequency in the high frequency portion of the band, at'- tenuating in a laterstage of the amplifier low frequency currents to produce uniform amplifica- .ton at all frequencies below said high frequency portion of the band and thereafter accentuating the voltages having frequencies in said high frequency portion of the band by an amount sufficient to overcome the attenuation produced by said shunt resistance and capacity in said high frequency portion of the band, said accentuation occurring at a point of said amplifier subsequent to a stage following the point where said low frequency accentuation occurs thereby to avoid overloading said last mentioned stage with curf rents to be attenuated.

2. In an amplifier for producing uniform ratio between input current and output voltage, said amplifier having resistance and capacity in shunt with its input to which said current is supplied. said current having frequencies extending over a wide band, the method which comprises attenuating currents in the intermediate frequency portion of said band above the frequency of .the most intense noise currents of the amplifier Without changing the characteristic relation between intensity of voltage on said resistance and capacity and frequency in the high frequency portion of the'band. amplifying the entire band, reduc'- ing the voltages having frequencies below said high frequency portion of the band to uniform intensity, again amplifying the entire band, and

- thereafter accentuating the voltages in the high frequency portion of said band sufficiently to overcome the effect. of said shunt resistance and' capacity in sai-d high frequencyv portion of the band.

3. The combination, in an amplifier for electromotive forces existing. across a capacitance at the input to said amplifier, said electromotive force having frequencies extending,over a wide band and having intensity at low 'frequencies only slightly above the level of undesired low frequency currents, of a resistance across said capacity. a portion of said resistance being shunted by a second capacity, said portion and V cies.

4. The combination, in a multistage amplifier,

va circuit atthe input to one of the stages of saidaxnpliflerlhaving shunt resistance and capacity producing attenuation of high frequency currents in the band to be amplified, a circuit between stages in said amplifier having shunt resistance and capacity, an inductance in series with said last resistance, said inductance and said resistance having a time constant equal to the time constant of said first mentioned shunt resistance and capacity, a shunt combination of resistance and capacitance in series with said second mentioned shunt resistance proportioned .to reduce the attenuation caused by said inductance and the resistance in series with it of low frequency currents thereby to maintain the electromotive forces at said low frequencies above quencies as not materially to effect the transmission of high frequency currents.

7. In combination, an amplifier channel having shunt resistance and capacity to which current to be amplified is supplied, said current having such intensities and frequencies extending over a band so wide that the attenuating effect of said resistance and capacity at high frequency cannot be compensated in a single stage of said the noise level of the stage of said amplier 4 subsequent thereto.

5. 'I'he combination, in a multistage amplifier, a circuit at the input to one of the stages of said amplifier having shunt resistance and capacity producing attenuation of high frequency currents in the band to be amplified, a. circuit between stages in said amplifier having shunt resistance .and capacity, an inductance in series with said last resistance, said inductance and said resistance having a time constant equal to the time constant'of said rst mentioned shunt resistance and capacity, a shunt combination of. resistance and capacitance in series with said second mentioned shunt resistance proportioned to reduce the attenuation produced by said inductance and the resistance in series with it of low frequency currents thereby to maintain the electromotive forces at said low frequencies above the noise level of the stage of said amplier subsequent thereto, and means later in said amplifier to attenuate the low frequency currents to a level of the high frequency currents.

6. The-combination, in an amplification channel for currents having frequencies extending over a. wide band, the high frequency 'currents insaid band being 4attenuated by the eil'ect of capacity and resistance in shunt to said channel, of an amplifier having' an output circuit having impedance at said high frequencies determined by an inductanceland resistance in sexies across amplifier 4without undesirably reducing the intensity level of electromotive force acrom said resistance and capacity, of means to produce a. uniform application ratio over a band of frequencies intermediate in said rst mentioned band,

, and means, thereafter, to compensate the variation in amplification of said amplifier with respect to frequency over the portion of said band below said intermediate portion, and a subsequent stage of said amplifier having means to compensate the variation in amplification over the portion of the band above said intermediate frequency portion, thereby to produce uniform amplification over the entire'band,

8. The combination, in a. wide ,band amplier having resistance and capacity in shunt with the input thereof and additional capacity shunting a portion of said resistance, and having an-interstage network comprising an interstage coupling capacity shunted by a. second resistance and having ,shunt resistance at either side of said coupling capacity, saidflrstresistance, said portion and said additional capacity being proportioned to accentuate low frequency current with respect to current of intermediate frequency in the band to be amplified, and said coupling capacity, second resistance and-shunt resistances being proportioned relative to saidY quencies.

' 9. 'I'he combination, in-a wide band amplifier 1 i having resistance and capacity in shunt withthe input thereof, and additional capacity shunting a portion of said resistance, and having an interstage network comprising a coupling capacity shunted by,a second resistance and having shunt resistance at either side of said coupling ca.- pacity, the ratio of the sum of said shunt resistances to `that part of said rst resistance not shunted by said additional capacity being equal to the ratio of said second resistance to said portion of said first resistance, and these ratios both being equal to the ratio of said additional capacity to said coupling capacity 10. The combination, in a. ,wide band amplifier havingresistance and capacity in shunt with the input thereof, and additional capacity shunting a portion of saidlresistance, and having an interstage network comprising an nterstage coupling capacity shunted by a second resistance and having shunt resistance at either side of said co1:-Y pling capacity, the ratio of the sum of saidshunt fier subsequent to said network amplifying the currents of all frequencies in said band, said amplifier including means to accentuate the high frequency currents sumciently tbscompensate for attenuation thereof produced by said rst resistcasos ance and capacity thereby to produce uniform vsirably attenuating high frequency currents in said band, which comprises the steps of rst accentuating low frequency currents in the band relative -to currents of intermediate frequency in said band, amplifying the entire band, attenuating said low frequency currents, again amplifying the entire band, accentuating low and high frequency currents relative to intermediate frequency currents, again amplifying the entire band and then attenuating said low frequency currents to produce uniform amplification at all frequencies in the band.

12. In a multistage amplifier for currents having frequencies extending over a wide band and having input capacity undesirably attenuating high frequency currents in said band, means in said input -circuit to. accentuate low frequency currents in said band to a level well above the low frequency noise level of the rst stage of said amplifier, means to attenuate said low frequency currents in a part of said amplifier subsequent to said first stage sufficiently to permit amplificationl of the entire band in another stale of said amplifier without low frequency overloading of said other stage, means between said other stage and a third stageto accentuate both llow and high frequency currents in said band relative to currents of intermediate frequency, and means in said amplifier subsequentto said third stage to attenuate said low frequency currents to the level of said high frequency currents thereby to pro.- duce uniform amplification over said band.

13. A wide band amplifier having resistance in shunt with the input thereof and capacity shunting a portion of said resistance, and having an interstage network comprising an interstage coupling capacity shunted by a second resistance and i v having shunt resistance at either side of said coupling capacity, said first resistance. said portion and said .capacity shuntlng said portion being proportioned to accentuate current of low frequency within a predetermined band to be amplified with respect to current of high frequencies in said predetermined band, and said coupling capacity. second resistance and shunt resistances being proportioned relative to said "capacity shuntlng said portion, -said portion and said rst resistance to attenuate said low frequency currents to produce uniform amplification at all frequencies in said predetermined band.

14. A lwide band amplifier having resistance in lshunt with the input thereof, and capacity shunting a portion of said resistance, and having an interstage network comprising a coupling capacity shunted by a second resistance and having shunt resistance at either side of said coupling capacity, the ratio of the sum of said shunt resistances to that part of said first resistance not shunted by said capacity being equalto the ratio of said second resistance to said portion of said first resistance, and these ratios bothbeing equal to the ratio of said capacity shuntlng said-portion to said coupling capacity.

l5. In a Wide band amplifier, an input network and an output network, one of said networks comprising a shunt resistance and a capacity shunting a portion of said resistance, the other of said networkscomprising a coupling capacity shunted by a second resistance and having shunt resistances at eitherl side of said cou-- pling capacity, said first resistance. said portion and said capacity shuntlng said portion being proportioned to accentuate current qf low frequency within a predetermined band to be amplied with respect to current of high frequen- Vcies in said predetermined band, and said coupling capacity, second resistance and shunt resistances being proportioned relative to said capacity shunting said portion, said portion and said first resistance to attenuate said low frequency currents to produce uniform amplification at all frequencies in said predetermined band.

16. In a Wide band amplifier, an input network and an output network, one of said networks comprising a shunt resistance and a capacity shunting a portion of said resistancel the other of said networks comprising a coupling capacity shunted' by a second resistance and hav- -ing shunt resistances at either side Vof said coupling capacity, the ratio of the sum of said last said portion of said first mentioned resistance, and these ratios both being equal to the ratio of said capacity shunting said portion to said coupling capacity. i n

DONALD E. NORGAARD. 

